Curable composition for nanoimprinting and cured product

ABSTRACT

Disclosed is a curable composition for nanoimprinting, which includes one or more polymerizable monomers, in which one or more monofunctional radically polymerizable monomers occupy 90 percent by weight or more of the one or more polymerizable monomers, and the one or more monofunctional radically polymerizable monomers give a polymer having a glass transition temperature of 25° C. or higher. The one or more monofunctional radically polymerizable monomers are preferably at least one compound selected from (meth)acrylic ester compounds, styrenic compounds, and vinyl ether compounds.

TECHNICAL FIELD

The present invention relates to a curable composition fornanoimprinting, a cured product thereof, a method for producing a finestructure using the curable composition for nanoimprinting, and a finestructure obtained by the production method, which curable compositionis suitable particularly for the producing of a fine structure using ananoimprinting technique out of microlithography techniques.

BACKGROUND ART

The miniaturization of electronic components, for which a resolutiondown to the range of less than 1 μm is required, has been achievedsubstantially by photolithographic techniques. For a further higherresolution, miniaturization is being achieved by the progress ofimmersion lithography technologies using ArF having a short exposurewavelength as a light source. However, such technologies for forming apattern with a line width of 32 nm or less have more and more sufferedfrom problems such as line edge roughness depending on the physicalproperties of a resin to be used. On the other hand, the higher andhigher requirements with respect to resolution, wall slope, and aspectratio (ratio of height to resolution) result in a cost explosion in thecase of masks, mask aligners, steppers, and other apparatuses requiredfor photolithographic structuring. Among them, owing to their very highprice, modern steppers are a considerable cost factor in microchipproduction as a whole. Independently, there is an attempt to useshort-wave radiation, such as electron beams and X-rays, for achieving ahigher resolution. However, this technique still has many problems whenadopted to mass production.

Liquid crystal displays each generally employ two or more functionalfilms typically including a light guide, a prism sheet, a deflectorplate, and an anti-reflection film for satisfactory viewing angle andhigh brightness. However, to obtain these functions using films composedof a thermoplastic film, it is necessary that the thermoplastic resin isheated to a temperature around its glass transition temperature Tg, apattern is transferred thereto, the patterned thermoplastic resin iscooled to room temperature, from which the mold is removed, and theseoperations cause a problem in throughput. In contrast, a thermalimprinting technique through coating allows curing to be easilyperformed at lower temperatures and thereby enables a higher throughput.UV-based nanoimprint lithography (UV-NIL) is a technique according towhich patterning is performed by applying a liquid photocurable resin toa substrate at room temperature; stamping an optically transparent moldonto the applied resin; and applying an ultraviolet ray (UV) to cure theresin on the substrate to form a pattern. This technique enables patterntransfer at room temperature and is expected typically for (i) a highthroughput and (ii) pattern transfer with high resolution or definition.However, if the expensive mold is contaminated with the liquid UV-NILmaterial during microprocessing, it is very difficult to recycle orreuse the mold, because the liquid UV-NIL material is cured through UVcuring into a solid that is insoluble in solvents.

U.S. Pat. No. 5,772,905 discloses a nanoimprinting process as a processfor forming a fine convexo-concave pattern on a film. This processapplies thermoplastic deformation to a resist using a relief-formedrigid stamp, which resist is applied to the entire surface of asubstrate (wafer) and is composed of a thermoplastic resin. This processemploys a thermoplastic resin (poly(methyl methacrylate), PMMA) as ahot-stamping resist. However, owing to common thickness variations ofabout 100 nm over the entire wafer surface, it is not possible tostructure a 6-, 8-, or 12-inch wafer in one step with a rigid stamp.Thus, a complicated “step and repeat” method would have to be used,which, however, is unsuitable in consideration of production process,owing to the reheating of already structured neighboring areas.

Japanese Unexamined Patent Application Publication (JP-A) No.2007-186570 discloses, as a process for forming a fine pattern throughUV-based nanoimprinting, a process of using a composition which containsa (meth)acrylate monomer having an alicyclic functional group and showssatisfactory dry etching resistance. This process, however, stillsuffers from a problem that a cured product of the composition isdifficult to be removed from the mold when the mold is contaminated withthe composition, because the multifunctional monomer has beenthree-dimensionally cured.

Japanese Unexamined Patent Application Publication (JP-A) No. 2007-1250reports another nanoimprinting technique as a process for forming a finepattern through nanoimprinting, in which a fluorocarbon polymer is usedfor improved mold releasability. This technique reduces the frequency ofmold contamination but still insufficiently, and the problem in removalof the cured product upon mold contamination still remains as asignificant problem.

Independently, an imprinting technique using an alkali-developableresist enables mold recycling or reusing. However, though beingeffective typically for peeling off of the cured article (fine pattern)from the mold, the alkali-developable resist is very difficult to beremoved from the fine pattern through dissolution, because a resinconstituting the resist is not thoroughly dissolved in an alkali but issuspended therein.

CITATION LIST Patent Literature

-   PTL 1: U.S. Pat. No. 5,772,905-   PTL 2: Japanese Unexamined Patent Application Publication (JP-A) No.    2007-186570-   PTL 3: Japanese Unexamined Patent Application Publication (JP-A) No.    2007-1250

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a curable compositionfor nanoimprinting which has sufficient curability, gives a curedproduct having satisfactory mold releasability (releasability from amold such as a transfer imprint stamp, a master mold, or a replica moldas a transfer target), and has satisfactory transferability, in whichthe cured product can be dissolved and thereby removed by the action ofan organic solvent or aqueous alkali solution according to necessity.Another object of the present invention is to provide a cured productobtained from the curable composition; a method for producing a finestructure using the curable composition for nanoimprinting, and a finestructure produced by the method.

Solution to Problem

After intensive investigations to achieve the objects, the presentinventors have found that a specific composition, when used as a curablecomposition for nanoimprinting, has sufficient curability, satisfactorymold releasability of a cured product thereof, and excellenttransferability, in which the cured product can be dissolved and therebyremoved by the action of an organic solvent or aqueous alkali solutionaccording to necessity, which specific composition contains at least onepolymerizable monomer, in which the polymerizable monomer includes 90percent by weight or more of one or more monofunctional radicallypolymerizable monomers, and the one or more monofunctional radicallypolymerizable monomers give a polymer having a glass transitiontemperature of 25° C. or higher. The present invention has been madebased on these findings.

Specifically, the present invention provides, in an aspect, a curablecomposition for nanoimprinting, comprising one or more polymerizablemonomers, wherein the one or more polymerizable monomers includes 90percent by weight or more of one or more monofunctional radicallypolymerizable monomers, and wherein the one or more monofunctionalradically polymerizable monomers give a polymer having a glasstransition temperature of 25° C. or higher.

The one or more monofunctional radically polymerizable monomers may beat least one compound selected from the group consisting of(meth)acrylic ester compounds, styrenic compounds, and vinyl ethercompounds.

At least one radically polymerizable monomer intramolecularly having acyclic structure is preferably used as the one or more monofunctionalradically polymerizable monomers. The radically polymerizable monomerintramolecularly having a cyclic structure may be at least one compoundselected from the group consisting of compounds represented by followingFormulae (1) to (3):

wherein R⁴¹, R⁴², and R⁴³ are the same as or different from one anotherand each represent —H or —CH₃.

At least one radically polymerizable monomer having a hydrophilic groupis also preferably used as the monofunctional radically polymerizablemonomers. Exemplary hydrophilic groups in the radically polymerizablemonomer having a hydrophilic group include hydroxyl groups, carboxylgroups, quaternary ammonium groups, amino groups, and heterocyclicgroups.

The curable composition for nanoimprinting may further include a polymerbeing obtained through polymerization of one or more monofunctionalradically polymerizable monomers and having a glass transitiontemperature of 25° C. or higher.

The curable composition for nanoimprinting may further include aradical-polymerization initiator.

The present invention provides, in another aspect, a cured productobtained through curing of the curable composition for nanoimprinting.

The present invention further provides, in yet another aspect, a methodfor producing a fine structure, the method including the step ofsubjecting the curable composition for nanoimprinting to give a finestructure.

The method for producing a fine structure may include the steps of (1)forming on a substrate a film from the curable composition fornanoimprinting as claimed in any one of claims 1 to 8; (2) stamping animprint stamp onto the film to transfer a pattern to the film; and (3)curing the pattern-transferred film to give a fine structure.

The imprint stamp used in Step (2) may be composed of at least oneselected from the group consisting of a silicone, glass, and silicaglass as a material.

The method may include, as Steps (2) and (3), the step of stamping theimprint stamp onto the film at a pressure of 10 kPa to 100 MPa for 0.01to 300 seconds to transfer the pattern to the film and simultaneouslyapplying heating and/or ultraviolet irradiation to the film to cure thefilm, to thereby give a fine structure.

The method for producing a fine structure may further include the stepof (4) etching the cured film; and/or may further include the step of(5) forming, on the resulting fine structure, a second structure fromanother material than that of the fine structure and subsequentlyremoving the fine structure to give a three-dimensional fine structure.The removal of the fine structure may be performed by dissolving thefine structure in a solvent or alkaline developer which dissolves notthe second structure but the fine structure.

The present invention provides, in still another aspect, a finestructure produced by the method.

Examples of the fine structure include materials for semiconductordevices, materials for micro-electric-mechanical systems, flat screens,holograms, waveguides, precision machinery components, sensors, andmolds for the production of replica molds.

Advantageous Effects of Invention

Curable compositions for nanoimprinting according to the presentinvention each have sufficient curability and satisfactory moldreleasability of a cured product thereof and show excellenttransferability, in which the cured product can be dissolved and therebyremoved by the action of an organic solvent or aqueous alkali solution(alkaline developer). The curable compositions are useful as a resistfor microstructuring of materials for semiconductor devices, materialsfor micro-electric-mechanical systems (MEMS), flat screens, holograms,waveguides, precision machinery components, sensors, or molds for theproduction of replica molds.

DESCRIPTION OF EMBODIMENTS

Curable compositions for nanoimprinting according to the presentinvention each contain one or more polymerizable monomers. A variety ofmonomers may be used as the polymerizable monomers herein, but it isimportant that the polymerizable monomers include 90 percent by weightor more (preferably 95 percent by weight or more) of one or moremonofunctional (having only one radically reactive unsaturated group)radically polymerizable monomers; and that the one or moremonofunctional radically polymerizable monomers give a polymer having aglass transition temperature of 25° C. or higher (preferably 40° C. orhigher). The curable composition, if containing monofunctional radicallypolymerizable monomers in an excessively small amount and containingmultifunctional radically polymerizable monomers in an excessively largeamount, gives a cured product being inferior in mold releasability,solubility in a solvent, and solubility in an alkaline developer, andthis impedes the removal of the cured product from the mold, to whichthe cured product has adhered. If the one or more monofunctionalradically polymerizable monomers give a polymer having a glasstransition temperature of lower than 25° C., the cured product showsinsufficient transferability and mold releasability, and the curablecomposition may be cured insufficiently.

Exemplary monofunctional radically polymerizable monomers include(meth)acrylic acid alkyl esters [e.g., (meth)acrylic acid alkyl esterswhose alkyl moiety having 1 to 10 carbon atoms], such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, pentyl (meth)acrylate, and hexyl (meth)acrylate;(meth)acrylic esters each intramolecularly having a cyclic structure(aliphatic cyclic structure or aromatic cyclic structure), such asbenzyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopentyl(meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate,dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate,2-(dicyclopentenyloxy)ethyl (meth)acrylate, and2-(dicyclopentanyloxy)ethyl (meth)acrylate; styrenic compounds such asstyrene, vinyltoluene, and α-methylstyrene; and vinyl ether compoundssuch as methyl vinyl ether, butyl vinyl ether, and phenyl vinyl ether.

Exemplary monofunctional radically polymerizable monomers furtherinclude radically polymerizable monomers each having a hydrophilicgroup. Exemplary hydrophilic groups include hydroxyl group, carboxylgroup, quaternary ammonium group, amino group, and heterocyclic groups.Specific examples of radically polymerizable monomers each having ahydrophilic group include compounds each having a phenolic hydroxylgroup, such as hydroxystyrene; hydroxyl-containing (meth)acrylic esterssuch as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,hydroxybutyl (meth)acrylate, and caprolactone-modified 2-hydroxyethyl(meth)acrylate; alkoxypolyalkylene glycol (meth)acrylates such asmethoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, isooctyloxydiethylene glycol (meth)acrylate,phenoxytriethylene glycol (meth)acrylate, methoxytriethylene glycol(meth)acrylate, and methoxypolyethylene glycol (meth)acrylates;carboxyl-containing monomers such as (meth)acrylic acid andβ-carboxyethyl (meth)acrylate; lactone-modified derivatives ofunsaturated carboxylic acids, such as ε-caprolactone adduct of(meth)acrylic acid; compounds corresponding to the hydroxyl-containingmonomers, except for the addition of an acid anhydride; amino-containing(meth)acrylic esters such as 2-aminoethyl (meth)acrylate; andheterocyclic compounds (e.g., nitrogen-containing heterocycliccompounds) each having a vinyl group, such as 2-vinylpyrrolidone.

Among them, preferred as monofunctional radically polymerizable monomersare radically polymerizable monomers each intramolecularly having acyclic structure and giving a homopolymer having a high glass transitiontemperature, such as the (meth)acrylic esters each intramolecularlyhaving a cyclic structure (aliphatic cyclic structure or aromatic cyclicstructure); of which more preferred are (meth)acrylic esters each havinga bridged skeleton, such as dicyclopentanyl (meth)acrylate,dicyclopentenyl (meth)acrylate, 2-(dicyclopentenyloxy)ethyl(meth)acrylate, and 2-(dicyclopentanyloxy)ethyl (meth)acrylate. Aboveall, dicyclopentanyl methacrylates represented by Formula (1),dicyclopentanyloxyethyl methacrylates represented by Formula (2), anddicyclopentenyloxyethyl methacrylates represented by Formula (3) areparticularly preferred. Independently, radically polymerizable monomerseach having a hydrophilic group are also preferred as monofunctionalradically polymerizable monomers.

In an embodiment of the present invention, a curable compositioncontains a relatively large amount of one or more radicallypolymerizable monomers each containing a hydrophilic group (of which aphenolic hydroxyl group, a carboxyl group, and/or a heterocyclic groupis preferred). This curable composition gives a cured product which isreadily soluble in an alkaline developer. In this case, the curablecomposition may contain one or more radically polymerizable monomers ina content typically of 10 percent by weight or more based on the totalweight of polymerizable monomers. In another embodiment, a curablecomposition contains a relatively small amount of one or more radicallypolymerizable monomers containing a hydrophilic group (of which aphenolic hydroxyl group, a carboxyl group, and/or a heterocyclic groupis preferred). This curable composition gives a cured product which isreadily soluble in an organic solvent. In this case, the curablecomposition may contain one or more radically polymerizable monomers ina content typically of less than 10 percent by weight based on the totalweight of polymerizable monomers. Examples of the organic solventinclude cyclic ethers such as tetrahydrofuran and dioxane; ketones suchas methyl ethyl ketone and cyclohexanone; glycol ethers such asCellosolve (ethylene glycol monoethyl ether), methyl Cellosolve(ethylene glycol monomethyl ether), Carbitol (diethylene glycolmonoethyl ether), methyl Carbitol (diethylene glycol monomethyl ether),butyl Carbitol (diethylene glycol monobutyl ether), propylene glycolmonomethyl ether, dipropylene glycol monomethyl ether, dipropyleneglycol monoethyl ether, and triethylene glycol monoethyl ether; aceticesters such as ethyl acetate, butyl acetate, Cellosolve acetate(ethylene glycol monoethyl ether acetate), butyl Cellosolve acetate(ethylene glycol monobutyl ether acetate), Carbitol acetate (diethyleneglycol ethyl ether acetate), butyl Carbitol acetate (diethylene glycolbutyl ether acetate), and propylene glycol monomethyl ether acetate; andalcohols such as ethanol, propanol, ethylene glycol, and propyleneglycol.

The one or more monofunctional radically polymerizable monomers hereinare chosen so that they give a polymer having a glass transitiontemperature of 25° C. or higher (e.g., from 25° C. to 220° C.) andparticularly preferably 40° C. or higher (e.g., from 40° C. to 220° C.).The glass transition temperature of the polymer may be determined bycalculation according to a known procedure. The glass transitiontemperature may also be determined by differential scanning calorimetry(DSC).

Particularly preferred embodiments of curable compositions fornanoimprinting according to the present invention include (1) a curablecomposition in which one or more monofunctional (meth)acrylic esterseach intramolecularly having a cyclic structure (of which an aliphaticcyclic structure is preferred) occupy 40 percent by weight or more, morepreferably 50 percent by weight or more, and particularly preferably 60percent by weight or more, of the total weight of polymerizable monomersin the curable composition; (2) a curable composition in which one ormore monomers selected from the group consisting ofphenolic-hydroxyl-containing monofunctional radically polymerizablemonomers, carboxyl-containing monofunctional radically polymerizablemonomers, and heterocyclic-group-containing monofunctional radicallypolymerizable monomers occupy 10 percent by weight or more, morepreferably 15 percent by weight or more, and particularly preferably 20percent by weight or more, of the total weight of polymerizable monomersin the curable composition; and (3) a curable composition which containsone or more monofunctional (meth)acrylic esters each intramolecularlyhaving a cyclic structure [of which monofunctional (meth)acrylic esterseach intramolecularly having an aliphatic cyclic structure (particularlya bridged skeleton) are preferred], in which one or more monomersselected from the group consisting of phenolic-hydroxyl-containingmonofunctional radically polymerizable monomers, carboxyl-containingmonofunctional radically polymerizable monomers, andheterocyclic-group-containing monofunctional radically polymerizablemonomers occupy 10 percent by weight or more, more preferably 15 percentby weight or more, and particularly preferably 20 percent by weight ormore, of the total weight of polymerizable monomers in the curablecomposition.

In an embodiment of the present invention, a curable composition fornanoimprinting may further contain a polymer which is obtained throughpolymerization of one or more monofunctional radically polymerizablemonomers and which has a glass transition temperature of 25° C. orhigher (e.g., from 25° C. to 220° C.), and preferably 40° C. or higher(e.g., from 40° C. to 220° C.). The composition, by containing such apolymer, may exhibit higher coatability.

The one or more monofunctional radically polymerizable monomers asmonomers for constituting the polymer may be those listed above.

The curable composition may contain the polymer in a content ofgenerally from about 0 to about 60 percent by weight (e.g., from about 3to about 60 percent by weight), preferably from about 0 to about 50percent by weight (e.g., from about 3 to about 50 percent by weight),and more preferably from about 0 to about 40 percent by weight (e.g., 5to about 40 percent by weight), based on the total weight of themonofunctional radically polymerizable monomers and the polymer.

In another embodiment of the present invention, a curable compositionfor nanoimprinting may further contain a radical-polymerizationinitiator. Exemplary radical-polymerization initiators include benzoinand benzoin alkyl ethers such as benzoin, benzoin methyl ether, benzoinethyl ether, and benzoin isopropyl ether; acetophenones such asacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, and2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one;anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone, and2-amylanthraquinone; thioxanthones such as 2,4-dimethylthioxanthone,2,4-diethylthioxanthone, 2-chlorothioxanthone, and2,4-isopropylthioxanthone; ketals such as acetophenone dimethyl ketaland benzyl dimethyl ketal; benzophenones such as benzophenone;xanthones; 1,7-bis(9-acridinyl)heptane; and other known or customaryphotoinitiators. Each of different photoinitiators may be used alone orin combination.

Each of these radical-polymerization initiators may be used incombination with one or more known or common photosensitizers. Exemplaryphotosensitizers include tertiary amines such as ethylN,N-dimethylaminobenzoate, isoamyl N,N-dimethylaminobenzoate, pentyl4-dimethylaminobenzoate, triethylamine, and triethanolamine.

Exemplary commercially available radical-polymerization initiatorsinclude photoinitiators including those of Irgacure (registeredtrademark) type each available from Ciba (now part of BASF), such asIrgacure (registered trademark) 184 (1-hydroxycyclohexyl phenyl ketone)and Irgacure (registered trademark) 500 (a mixture of1-hydroxycyclohexyl phenyl ketone and benzophenone); and Darocur(registered trademark) 1173, 1116, 1398, 1174, and 1020 each availablefrom Merck. Independently, examples of thermal (polymerization)initiators suitable for use herein include organic peroxides, of whichpreferred are organic peroxides in the form of diacyl peroxides,peroxydicarbonates, alkyl peresters, dialkyl peroxides, perketals,ketone peroxides, and alkyl hydroperoxides. Specific examples of suchthermal initiators include dibenzoyl peroxide, t-butyl perbenzoate, andazobisisobutyronitrile.

In yet another embodiment of the present invention, a curablecomposition for nanoimprinting may contain one or more fluorochemical orsilicone surfactants. Among them, fluorochemical surfactants areeffective for improved mold releasability, thus being preferred. Offluorochemical surfactants (fluorine-containing surfactants), preferredare anionic fluorine-containing surfactants, cationicfluorine-containing surfactants, amphoteric fluorine-containingsurfactants, or nonionic fluorine-containing surfactants. Thesefluorine-containing surfactants may be either hydrophobic orwater-soluble. Typically, exemplary anionic fluorine-containingsurfactants include Surflon S-111 (supplied by AGC Seimi Chemical Co.,Ltd.), Fluora FC-143 (supplied by Minnesota Mining & Manufacturing Co.(3M)), and Megafac F-114 (supplied by DIC Corporation). Exemplarycationic fluorine-containing surfactants include Surflon S-121 (suppliedby AGC Seimi Chemical Co., Ltd.), Fluora FC-134 (supplied by 3M), andMegafac F-150 (supplied by DIC Corporation). Exemplary amphotericfluorine-containing surfactants include Surflon S-132 (supplied by AGCSeimi Chemical Co., Ltd.), Fluora FX-172 (supplied by 3M), and MegafacF-120 (supplied by DIC Corporation). Exemplary nonionicfluorine-containing surfactants include Surflon S-145, S-393, KH-20, andKH-40 (supplied by AGC Seimi Chemical Co., Ltd.), Fluorad FC-170 andFC-430 (supplied by 3M), and Megafac F-141 (supplied by DICCorporation). Silicone surfactants for use herein may be any of knownsilicone surfactants.

Where necessary, a curable composition for nanoimprinting according tothe present invention may further contain any of, for example, resins(binder resins) other than the above resin, monomers, oligomers,sensitizers, and nano-scale particles (nanoparticles).

A method for producing a fine structure according to the presentinvention applies nanoimprinting to the curable composition fornanoimprinting according to the present invention and thereby yields afine structure. More specifically, the method according to the presentinvention includes the steps of (1) forming on a substrate a film fromthe curable composition for nanoimprinting according to the presentinvention; (2) stamping an imprint stamp onto the film to transfer apattern to the film; and (3) curing the pattern-transferred film to givea fine structure.

Examples of the substrate (support, carrier) to which the curablecomposition is applied in Step (1) include glass, silica glass, plasticfilms, and silicon wafers. Each of these substrates may have an adhesionpromoting film on its surface. The adhesion promoting film may be formedfrom an organic polymer which helps the substrate to have sufficientwetting with respect to the resin composition (curable composition).Exemplary organic polymers for constituting the adhesion promoting filminclude aromatic-compound-containing polymers or copolymers eachcontaining novolaks, styrenes, (poly)hydroxystyrenes and/or(meth)acrylates. The adhesion promoting film may be formed by applying asolution containing the organic polymer to the substrate according to aknown procedure such as spin coating.

The curable composition for nanoimprinting may be applied (coated) asintact or as a solution in an organic solvent. By using the organicsolvent, the composition is diluted into a paste, the paste easilyundergoes a coating process, and the applied paste is then dried to forma film which enables contact exposure. Exemplary organic solvents foruse herein include ketones such as methyl ethyl ketone andcyclohexanone; aromatic hydrocarbons such as toluene, xylenes, andtetramethylbenzene; glycol ethers such as Cellosolve, methyl Cellosolve,Carbitol, methyl Carbitol, butyl Carbitol, propylene glycol monomethylether, dipropylene glycol monomethyl ether, dipropylene glycol monoethylether, and triethylene glycol monoethyl ether; acetic esters such asethyl acetate, butyl acetate, Cellosolve acetate, butyl Cellosolveacetate, Carbitol acetate, butyl Carbitol acetate, and propylene glycolmonomethyl ether acetate; alcohols such as ethanol, propanol, ethyleneglycol, and propylene glycol; aliphatic hydrocarbons such as octane anddecane; and petroleum solvents such as petroleum ether, petroleumnaphtha, hydrogenated petroleum naphtha, and solvent naphtha. Each ofdifferent organic solvents may be used alone or in combination.

In Step (1), a film of the curable composition for nanoimprinting may beformed by applying the curable composition to the substrate according toa known procedure such as spin coating, slit coating, spray coating, orroller coating. The film (curable composition at coating) has aviscosity of preferably from about 1 mPa·s to about 10 Pa·s and morepreferably from about 1 mPa·s to about 1000 mPa·s. The thus-formed filmof the curable composition for nanoimprinting (film before curing) has athickness of typically from about 0.01 to about 1 μm, and preferablyfrom about 0.01 to about 0.5 μm.

The imprint stamp (nanostamper) for use in Step (2) may be a stamperwhich is a nanoimprinting-transfer stamp bearing a convexo-concavetransfer pattern on its surface and is composed of a material such as asilicone, glass, or silica glass. Among such stampers, a silicone rubberstamper is advantageously usable for satisfactory releasability from theresin after pattern transfer. Independently, a finely patterned metallicmold may also be used as the imprint stamp herein.

The pattern transfer in Step (2) is performed by stamping or pressingthe imprint stamp against the film at a pressure of from 10 kPa to 100MPa for a duration of typically from about 0.01 to about 300 seconds andpreferably from about 5 to about 150 seconds. The film after patterntransfer has a thickness of typically from about 50 to about 1000 nm andpreferably from about 150 to about 500 nm.

The curing process in Step (3) is preferably conducted such that thenanostamper is left stand on the film. In a preferred embodiment, themethod includes, as Steps (2) and (3), the step of stamping thenanostamper onto the film at a pressure of from 10 kPa to 100 MPa for0.01 to 300 seconds (preferably 5 to 150 seconds) to transfer thepattern to the film, and simultaneously with this, applying heatingand/or UV (ultraviolet ray) irradiation to the film to cure the film, tothereby yield a fine structure. The cured film after curing process hasa thickness of typically from about 50 to about 1000 nm and preferablyfrom about 150 to about 500 nm.

The film may be cured by a thermal curing process through heating, or anUV curing process through ultraviolet irradiation, or both incombination. The UV curing generally employs a transfer stamp havingultraviolet transparency. The thermal curing may be performed typicallyunder such conditions as to heat the film at a temperature of from about80° C. to about 150° C. for about 1 to about 10 minutes. The UV curingmay be performed typically under conditions as to apply an ultravioletray to the film for about 5 to about 20 minutes.

After the film is cured by the curing process, the imprint stamp isremoved according to necessity, and an imprinted fine structure(microstructure) is obtained.

An observation of the resulting fine structure under a scanning electronmicroscope reveals that the target substrate bears not only theimprinted fine structure but also an unstructured residual layer havinga thickness of less than 30 nm. When the fine structure will besubsequently used in a microelectronic device, the residual layer shouldbe removed for a steep wall slope and a high aspect ratio. To meet thisrequirement, the method preferably further includes the step of etchingthe cured film as Step (4).

The etching of the cured film (residual layer) in Step (4) may beconducted typically through dry etching with oxygen plasma or a CHF₃/O₂gas mixture. The etching may also be conducted through wet etching withan organic solvent (e.g., tetrahydrofuran) and/or an alkaline developer.Wet etching is easily performed according to the present invention,because the cured film is readily soluble in an organic solvent and/oran alkaline developer.

After etching, the resist coated film (resist film) may be removedtypically using an organic solvent (e.g., tetrahydrofuran) and/ortetramethylammonium hydroxide.

The fine structure may further be subjected to one or more suitableprocesses according to the type thereof so as to have desiredproperties.

The method according to the present invention may further include thestep of forming on the resulting fine structure a second structure fromanother material than that of the fine structure and subsequentlyremoving the fine structure to yield a three-dimensional fine structure,as Step (5). Such a three-dimensional fine structure may be easilyproduced by the above method according to the present invention, becausethe cured film is satisfactorily releasable from a mold (particularlyfrom a structure composed of a material different therefrom).

The removal of the fine structure may be conducted by dissolving thefine structure in a solvent or alkaline developer which dissolves notthe second structure but the fine structure therein. According to thepresent invention, such a three-dimensional fine structure may be easilyprepared, because the cured film is readily soluble in an organicsolvent and/or alkaline developer.

The method according to the present invention enables efficientproducing of a finely-patterned fine structure which excels incurability, transferability, and mold releasability, has satisfactorysolubility in a solvent and/or alkaline developer, and can thereby beproduced even in mass production through nanoimprinting technologies.The method also enables simple and easy producing of a three-dimensionalfine structure. The resulting fine structures are useful typically asmaterials for semiconductor devices, materials formicro-electric-mechanical systems, flat screens, holograms, waveguides,precision machinery components, sensors, and molds for the production ofreplica molds.

EXAMPLES

The present invention will be illustrated in further detail withreference to several working examples below. It should be noted,however, that these examples are never construed to limit the scope ofthe present invention.

Preparation Example 1 Synthesis of Polymer (A-1)

Cyclohexanone (125 g) was fed into a 1-liter separable flask equippedwith a stirrer, a thermometer, a reflux condenser, dropping funnels, anda nitrogen inlet tube, and heated to 95° C., to which 150 g ofdicyclopentanyl methacrylate (“FA-513M” supplied by Hitachi Chemical.Co., Ltd.), 6 g of 2,2′-azobis(2-methylbutyronitrile) (“ABN-E” suppliedby Japan Hydrazine Co., Inc. (now Japan Finechem Company, Inc.)), and212 g of cyclohexanone were added dropwise together over 3 hours. Afterthe dropwise addition, the mixture was aged for 4 hours and therebyyielded a target Polymer (A-1). The resulting polymer had a glasstransition temperature Tg of 175° C.

Preparation Example 2 Synthesis of Polymer (A-2)

Cyclohexanone (125 g) was fed into a 1-liter separable flask equippedwith a stirrer, a thermometer, a reflux condenser, dropping funnels, anda nitrogen inlet tube and heated to 95° C., to which 138 g ofdicyclopentanyl methacrylate (“FA-513M” supplied by Hitachi ChemicalCo., Ltd.), 12.2 g of methacrylic acid, 4 g of2,2′-azobis(2-methylbutyronitrile) (“ABN-E” supplied by Japan HydrazineCo., Inc. (now Japan Finechem Company, Inc.)), and 212 g ofcyclohexanone were added dropwise together over 3 hours. After thedropwise addition, the mixture was aged for 4 hours and thereby yieldeda target Polymer (A-2). The resulting polymer had a glass transitiontemperature Tg of 140° C. and an acid value (acid number) of 60KOH-mg/g.

Preparation Example 3 Synthesis of Polymer (A-3)

Propylene glycol monomethyl ether (“MMPG” supplied by Daicel ChemicalIndustries, Ltd.) (300 g) was fed into a 2-liter separable flaskequipped with a stirrer, a thermometer, a reflux condenser, droppingfunnels, and a nitrogen inlet tube, and heated to 110° C., to which 151g of methacrylic acid, 110 g of methyl methacrylate, 200 g of MMPG, and28.7 g of t-butyl peroxy-2-ethylhexanoate (“PERBUTYL O” supplied by NOFCorporation) were added dropwise together over 3 hours. After thedropwise addition, the mixture was aged for 4 hours and therebysynthetically yielded a trunk polymer containing carboxyl groups. Next,the trunk polymer solution was combined with 239 g of3,4-epoxycyclohexylmethyl acrylate (“CYCLOMER A200” supplied by DaicelChemical Industries, Ltd.), 2.4 g of triphenylphosphine, and 1.0 g ofmethylhydroquinone, followed by a reaction at 100° C. for 10 hours. Thereaction was performed in an atmosphere of mixture of air and nitrogen.This gave a target Polymer (A-3). The resulting polymer had a glasstransition temperature Tg of 105° C., an acid value of 50 KOH-mg/g, anda double-bond equivalent (resin weight per 1 mol of unsaturated group)of 381.

Examples 1 to 12, Comparative Examples 1 to 4 Preparation of Film

A series of curable compositions for nanoimprinting was prepare byblending in a flask a resin, a monomer or monomers, and an initiator inthe types and amounts (parts by weight) given in a table below, and asolvent (cyclohexanone) in such an amount as to give a solids content of30 percent by weight. Specific compounds used as the respectivecomponents in the table are as follows.

Resin

A-1: Polymer obtained from Preparation Example 1

A-2: Polymer obtained from Preparation Example 2

A-3: Polymer obtained from Preparation Example 3

Monomer

B-1: EA-513M (supplied by Hitachi Chemical Co., Ltd.), dicyclopentanylmethacrylate)

B-2: FA-513A (supplied by Hitachi Chemical Co., Ltd.), dicyclopentanylacrylate)

B-3: FA-512A (supplied by Hitachi Chemical Co., Ltd.),dicyclopentenyloxyethyl acrylate)

B-4: FA-512M (supplied by Hitachi Chemical Co., Ltd.),dicyclopentenyloxyethyl methacrylate)

B-5: p-Hydroxystyrene

B-6: βCEA (supplied by Daicel-Cytec Co., Ltd., (β-carboxyethyl acrylate)

B-7: MAA (supplied by Nippon Shokubai Co, Ltd., methacrylic acid)

B-8: BA (butyl acrylate)

B-9: 2VP (supplied by Nippon Shokubai Co, Ltd., 2-vinylpyrrolidone)

B-10: 4EO-A (supplied by Osaka Organic Chemical Industry Ltd.,polyethylene glycol diacrylate)

B-11: TMPTA (trimethylolpropane triacrylate) Initiator

C-1: “Irgacure 907” supplied by Ciba Specialty Chemicals Corporation

Each of the resulting curable compositions for nanoimprinting wasapplied to a 4-inch silicon wafer, which had been pretreated withhexamethyldisilazane, by spin coating at 3000 revolutions for 30 secondsand thereby yielded a film thereon. Next, the film was subjected to adrying process for the removal of the solvent by heating at about 80° C.for 5 minutes. The film after drying had a thickness of about 200 nm.

An imprinter used herein was a computerized tester (“Model NM-0401”supplied by Meisho Kiko Co.). This apparatus is capable of maintaining apredetermined pressure for a specific duration by programming conditionsor parameters such as loading, relaxation rate, and heating temperature.Nanoimprinting was performed on the film as examples and comparativeexamples using a transfer imprint stamp bearing a 200-nm line-and-spacepattern under the conditions given in the table below (stampingpressure: 2 MPa, stamping temperature: 25° C., stamping time: 60 sec).

Next, while the transfer imprint stamp was being in contact with thefilm, a curing process was applied to the film by applying ultravioletradiation (ultraviolet ray exposure energy: 1 J/cm²) to the film usingan attached high-pressure mercury lamp and thereby yielded a curedproduct bearing a fine pattern. The both ends of the pattern, therectangular shapes of the pattern edges, and the nanostructure (finestructure) having a wall slope of about 90° were observed under ascanning electron microscope, and properties or conditions of thenanostructure were evaluated based on the observed dimensions. Theevaluation results are shown in the table below.

Evaluations

(Coatability)

A sample curable composition was applied to a silicon wafer by spincoating to give a coated film, and the surface of the coated film wasobserved to find whether a uniform coated film was formed.

A: A uniform film was obtained.

C: Crawling of the coated film was observed after spin coating.

(Curability)

After imprinting, the surface of a sample film was observed to determinewhether the film was cured or not.

A: The film was uniformly cured.

B: The film was cured but showed unevenness.

C: The film showed stickiness and was not cured.

(Transferability)

After the transfer imprint stamp was removed, the formed pattern wasobserved under a scanning electron microscope to observe the appearanceof the pattern.

A: Pattern edges and pattern ends retained rectangular shapes.

B: Pattern edges and pattern ends were curved.

C: Pattern surfaces at both ends of the film shrank with peeling.

(Releasability from Transfer Imprint Stamp)

A sample coated film after exposure and curing was to be removed fromthe transfer imprint stamp, and at this time, the releasability of thefilm was observed.

A: The film could be easily removed merely by touching the imprintstamp.

B: The film could be removed by impressing a force upon the imprintstamp.

C: The film could not be easily removed bare-handed.

(Solvent Solubility)

After removing the transfer imprint stamp, the formed pattern wasimmersed in a solvent (THF; tetrahydrofuran), and the appearance of thepattern was observed. Likewise, the formed pattern was immersed in anaqueous alkali solution [2.38 percent by weight aqueous TMAH(trimethylammonium hydroxide) solution], and the appearance of thepattern was observed.

A: The pattern was thoroughly dissolved within 10 to 20 seconds.

B: The pattern was almost dissolved 2 minutes later but partiallyincluded undissolved residual matter.

C: The pattern was not dissolved at all.

The glass transition temperature Tg (° C.) in the table represents aglass transition temperature Tg as calculated from the copolymer ofcorresponding monomers. When a multifunctional acrylate was used as partof monomers, the glass transition temperature Tg represents a glasstransition temperature Tg (estimate) of a polymer formed from the othermonomers than the multifunctional acrylate.

TABLE 1 Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Nanoimprintingcomposition Resin A-1 9.5 9 9 30 5 10 9 A-2 20 15 5 10 10 10 10 10 A-310 Monomer B-1 100 90.5 55 10 20 70 B-2 81 81 70 65 70 60 70 70 40 B-310 80 B-4 10 10 5 B-5 30 B-6 5 20 20 B-7 20 20 B-8 5 10 70 20 B-9 70B-10 5 30 B-11 30 Tg 175 175 104 110 132 148 141 114 88 98 140 175 10 −4175 62 Initiator C-1 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 Solids content % 3030 30 30 30 30 30 30 30 30 30 30 30 30 30 30 Imprinting conditionsStamping MPa 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 pressure Stamping ° C. 2525 25 25 25 25 25 25 25 25 25 25 25 25 25 25 temperature Stamping timeSec 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 UV exposure J/cm² 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Evaluation results Coatability B A A A A AA A A A A A A A A A Curability A A A A A A A A A A A A B A A ATransferability A A A A A A A A A A A A B C A C Releasability A A A A AA A A A A A A C C A C Solubility Solvent THF A A A A A A A A C C C C A CC C Aqueous alkali 2.38% C C C C C C C C A A A A C A C C solution TMAH

The table demonstrates that curable compositions for nanoimprintingaccording to the present invention excel in transferability and givecured products which have satisfactory releasability and are readilysoluble in a solvent (THF) or a 2.38 percent by weight aqueous TMAH(trimethylammonium hydroxide) solution as an aqueous alkali solution.

Example 13

A composition for imprinting was prepared by mixing 10 g of Polymer A-1,90 g of Monomer B-1, and an initiator Irg 907 (Irgacure 907) in anamount of 5 percent by weight based on the total weight, to give amixture; and filtering the mixture through a 0.05-micron mesh filter.The prepared curable composition for imprinting was dropped onto apolyethylene terephthalate) (PET) film; using the imprinter, a quartzmaster mold having a 200- to 1000-nm line-and-space and 500-nmnanopillar structure was placed on the applied curable composition; thetransfer pressure was increased to a pressure of 1 MPa over 30 seconds;and, while maintaining the transfer pressure, an ultraviolet ray wasapplied from the quartz mold side to cure the composition forimprinting. The master mold was removed, and thereby a fine-structurepattern composed of the cured product for nanoimprinting was obtained onthe PET film. Independently, a nanoimprinting material (NIAC 34;radically curable) supplied by Daicel Chemical Industries, Ltd. wasapplied to a glass substrate by spin coating, and prebaked at 85° C. for30 seconds, onto which the fine pattern formed on the PET film wastransferred using the imprinter. After transferring, the PET film wasremoved, the cured product for nanoimprinting, being soluble in asolvent, was dissolved through immersion in cyclohexanone, and thereby areplica mold was prepared. Observations of the pattern dimensions of theprepared replica mold and the dimensions of the master mold under anatomic force microscope (AFM) revealed that the prepared replica moldhad pattern dimensions substantially equivalent to those of the mastermold.

Example 14

A fine-structure pattern was formed on a PET film by the procedure ofExample 13. Next, a nanoimprinting material (NIHB 34; a hybrid materialbeing both radically curable and cationically curable) supplied byDaicel Chemical Industries, Ltd. was applied to a glass substrate byspin coating, to which the fine pattern formed on the PET film wastransferred using the imprinter. After transferring, the PET film wasremoved, the cured product for nanoimprinting, being soluble in asolvent, was dissolved by immersing in cyclohexanone, and a replica moldwas thus prepared. Observations of the pattern dimensions of theprepared replica mold and the dimensions of the master mold under anatomic force microscope (AFM) revealed that the prepared replica moldhad pattern dimensions substantially equivalent to those of the mastermold.

Example 15

A fine-structure pattern was formed on a PET film by the procedure ofExample 13. Next, a nanoimprinting material (NICT 39; cationicallycurable) supplied by Daicel Chemical Industries, Ltd. was applied to aglass substrate by spin coating, to which the fine pattern formed on thePET film was transferred using the imprinter. After transferring, thePET film was removed, and there was found a solvent-developable resin(fine-structure pattern composed of the cured product fornanoimprinting) on the PET film. Thus, a replica mold was preparedwithout dissolving the solvent-soluble cured product for nanoimprinting.Observations of the pattern dimensions of the prepared replica mold andthe dimensions of the master mold under an atomic force microscope (AFM)revealed that the prepared replica mold had pattern dimensionssubstantially equivalent to those of the master mold.

INDUSTRIAL APPLICABILITY

The curable compositions for nanoimprinting according to the presentinvention excel in curability, transferability, and mold releasability,have satisfactory solubility in a solvent and/or an alkaline developer,enable mass production according to nanoimprinting technologies, andenable efficient production of fine structures each bearing a finepattern. The curable compositions also enable easy and simple productionof three-dimensional fine structures. The resulting fine structures areuseful typically as materials for semiconductor devices, materials formicro-electric-mechanical systems (MEMS), flat screens, holograms,waveguides, precision machinery components, sensors, or molds for theproduction of replica molds.

1. A curable composition for nanoimprinting, comprising one or morepolymerizable monomers, wherein the one or more polymerizable monomersincludes 90 percent by weight or more of one or more monofunctionalradically polymerizable monomers, and wherein the one or moremonofunctional radically polymerizable monomers give a polymer having aglass transition temperature of 25° C. or higher.
 2. The curablecomposition for nanoimprinting according to claim 1, wherein the one ormore monofunctional radically polymerizable monomers are at least onecompound selected from the group consisting of (meth)acrylic estercompounds, styrenic compounds, and vinyl ether compounds.
 3. The curablecomposition for nanoimprinting according to claim 1 or 2, comprising atleast one radically polymerizable monomer intramolecularly having acyclic structure as the one or more monofunctional radicallypolymerizable monomers.
 4. The curable composition for nanoimprintingaccording to claim 3, wherein the at least one radically polymerizablemonomer intramolecularly having a cyclic structure is at least onecompound selected from the group consisting of compounds represented byfollowing Formulae (1) to (3):

wherein R⁴¹, R⁴², and R⁴³ are the same as or different from one anotherand each represent —H or —CH₃.
 5. The curable composition fornanoimprinting according to claim 1 or 2, comprising at least oneradically polymerizable monomer having a hydrophilic group as the one ormore monofunctional radically polymerizable monomers.
 6. The curablecomposition for nanoimprinting according to claim 5, wherein thehydrophilic group of the at least one radically polymerizable monomerhaving a hydrophilic group is hydroxyl group, carboxyl group, quaternaryammonium group, amino group, or a heterocyclic group.
 7. The curablecomposition for nanoimprinting according to claim 1, further comprisingat least one polymer being obtained through polymerization of one ormore monofunctional radically polymerizable monomers and having a glasstransition temperature of 25° C. or higher.
 8. The curable compositionfor nanoimprinting according to claim 1, further comprising at least oneradical-polymerization initiator.
 9. A cured product obtained throughcuring of the curable composition for nanoimprinting as claimed inclaim
 1. 10. A method for producing a fine structure, the methodcomprising the step of nanoimprinting the curable composition fornanoimprinting as claimed in claim 1 to give a fine structure.
 11. Themethod for producing a fine structure, according to claim 10, the methodcomprising the steps of (1) forming on a substrate a film from thecurable composition for nanoimprinting; (2) stamping an imprint stamponto the film to transfer a pattern to the film; and (3) curing thepattern-transferred film to give a fine structure.
 12. The method forproducing a fine structure, according to claim 11, wherein the imprintstamp used in Step (2) comprises at least one selected from the groupconsisting of a silicone, glass, and silica glass as a material.
 13. Themethod for producing a fine structure, according to claim 11, whereinthe method comprises, as Steps (2) and (3), the step of stamping theimprint stamp onto the film at a pressure of 10 kPa to 100 MPa for 0.01to 300 seconds to transfer the pattern to the film and simultaneouslyapplying heating and/or ultraviolet irradiation to the film to cure thefilm, to thereby give a fine structure.
 14. The method for producing afine structure, according to claim 11, further comprising the step of(4) etching the cured film.
 15. The method for producing a finestructure, according to claim 11, further comprising the step of (5)forming, on the resulting fine structure, a second structure fromanother material than that of the fine structure and subsequentlyremoving the fine structure to give a three-dimensional fine structure.16. The method for producing a fine structure, according to claim 15,wherein the removal of the fine structure is performed by dissolving thefine structure in a solvent or alkaline developer which dissolves notthe second structure but the fine structure.
 17. A fine structureproduced by the method as claimed in claim
 10. 18. The fine structureaccording to claim 17, as a material for semiconductor devices, amaterial for micro-electric-mechanical systems (MEMS), a flat screen, ahologram, a waveguide, a precision machinery component, a sensor, or amold for the production of a replica mold.